The prior art comprises packaging lines equipped with two or more picking devices, also called pickers. Said devices or pickers can be represented for example by robots with two or more degrees of freedom. A suitable robot for these applications is for example the delta robot known from U.S. Pat. No. 4,976,582.
The task of said picking devices is to pick items from at least one inlet conveyor and transfer them into a predetermined location on at least one second outlet conveyor. Normally, bulk products are carried by the inlet conveyor with a well-ordered or a random arrangement, depending on the production cycle; the outlet conveyor carries a series of containers or boxes adapted to receive one or more items each.
The picking devices are often located above the conveyors, which is commonly referred to as top-loading arrangement.
Operations carried out by a picking device are called missions. Hence, picking missions and delivery missions are defined. A picking mission comprises picking an item, or many items as the case may be, from one location or several locations of the first inlet conveyor. A delivery mission comprises delivery of item or items (picked in a previous mission) in a desired location of the second outlet conveyor, for example inside a container.
In the following description, the term “robot” will be used for conciseness to indicate the picking devices. The term robot shall be intended to mean a device suitable for picking and delivering the items.
The missions are governed by a control system. In basic terms, the control system has at any time a certain number of picking locations and a certain number of delivery locations. Said picking and delivery locations are predetermined or dynamically detected for example with a viewing system. The control system continuously receives “requests” from the robots: for example a free robot issues a request for a picking mission, whereas a robot holding an article, just after execution of a picking mission, issues a delivery request.
The control system is substantially a manager of said requests, and allocates respective pickup locations, or delivery locations, to the robots. The criteria for allocation may include: picking all the incoming items; filling all locations of the second conveyor, according to the required format, avoiding gaps in the output; reducing waiting time of the robots. The pickup locations correspond to the locations (coordinates) of the items; the delivery locations correspond for example to free spaces inside containers.
Each of the robots operates inside its own working area, which corresponds to a region of the first and second conveyor, respectively, the robot is physically able to reach with its gripping member.
In the prior art, the robots are spaced apart so that the respective working areas have no point in common. The absence of shared working areas simplifies the control but results in some drawbacks including a longer and/or wider packaging line. Moreover, the working areas are usually roughly circular; in other words the areas are defined by circles without points in common or at most tangent. Said configuration generates relatively large “dark” areas around the points of tangency, which cannot be reached by any of the robots.
Large dark areas have a negative effect on the rate of occupation of the robots, because a free item or a free delivery location, while passing through a dark area, cannot be allocated to any robot. As each robot operates exclusively in its own working area, such an arrangement is also less adaptive to fluctuations of the feed, i.e. to fluctuations of the number of incoming items per minute. In such conditions some robots of the line are full- or even over-loaded, whilst other robots are underutilized. This problem is also suffered during a transient, for example start-up of the line or stop/start of an upstream machine that delivers the items.
In order to overcome these limitations, there is a need to bring robots closer to each other, thus bringing the respective working areas to partially overlap one another and creating one or more shared working areas. Shared working areas are defined as regions of the first conveyor and/or of the second conveyor where at least two different robots can operate. This realization, however, needs an anti-collision control.
Known anti-collision control systems in the field of robotics have been developed substantially for safety purposes, to avoid damage of the robots or to avoid interference of a robot with fixed structures or human beings in the vicinity. Basically, said anti-collision systems intervene when a moving part of the robot enters a forbidden area. Said systems however are not satisfactory for application to packaging lines, since they do not allow optimisation of performance and, notably, they do not solve the problem of how to allocate the picking or delivery missions. The above mentioned requirements, including the picking of all incoming items, completion of outgoing packages, and balancing of the load between the robots, require to set suitable criteria for management of several picking devices (robots) with shared areas. This need becomes increasingly stringent as the market requires packaging machines capable of high flows [number of items/min] and adaptable to the change of format.
The prior art does not provide a satisfactory solution. It is still preferred to configure robots with separate working areas or at most tangent working areas. This is a simple solution since it is sufficient to configure each robot with a set of coordinates that define its working area, substantially independently from the working areas of the other robots. However, it suffers the above mentioned drawbacks.